PCI Express

PCI Express is a serial connection that operates more like a network than a bus. Instead of one bus that handles data from multiple sources, PCIe has a switch that controls several point-to-point serial connections. These connections fan out from the switch, leading directly to the devices where the data needs to go. Every device has its own dedicated connection, so devices no longer share bandwidth like they do on a normal bus.

PCI Express Lanes

When the computer starts up, PCIe determines which devices are plugged into the motherboard. It then identifies the links between the devices, creating a map of where traffic will go and negotiating the width of each link. This identification of devices and connections is the same protocol PCI uses, so PCIe does not require any changes to software or operating systems.Each lane of a PCI Express connection contains two pairs of wires — one to send and one to receive. Packets of data move across the lane at a rate of one bit per cycle. A x1 connection, the smallest PCIe connection, has one lane made up of four wires. It carries one bit per cycle in each direction. A x2 link contains eight wires and transmits two bits at once, a x4 link transmits four bits, and so on. Other configurations are x12, x16 and x32.Devices using PCI share a common bus, but each device using PCI Express has its own dedicated connection to the switch.
Below is a table comparing the main specifications for the expansion for expansion slots that ever exists for the PC.